When my charecter Roland discoverd this quest he was with another charecter, then by the time I was finished there was 3 of us. the quest can be done with one, but with large dire rat spawns at least two people makes sense to go that far into the sewer, and can make for interesting RP. so what i suggest is that the quest support parties as well, 3 people= 3 keys.
when i make my point on RP...doing that quest with 3 people and exploring after was one of my favorite experiences in two years i have been playing. i'm sure everyone involved in that experience would agree ^_^